(1) Field of the Invention
This invention relates to a switch device, in which information displayed on a screen of a display unit is seen through a transparent key-top, more specifically, to a switch device employing a seesaw-type key-top to be provided on an electronic display unit such as a liquid crystal display and an electro luminescent display.
(2) Description of the Related Art
Many switch devices having transparent key-tops through which information displayed on a screen of a display unit is seen, have hitherto been proposed. Some of these switch devices are disclosed in Japanese Patent Application laid-Open No. H644857, H7-64688, H8-235961 and H9-198176.
For example, as illustrated in FIG. 7, a conventional switch device 100 is constructed in a manner such that a transparent key-top 120 is arranged over a screen of a display unit 110, in which information 111 (for example, a symbol indicating a function allotted to the key-top 120) displayed on the screen of the display unit 110 can be seen through the key-top 120.
The key-top 120 is resiliently fitted into a case 130 using a spring and can be pushed downward. An image guide 121 (a block composed of bundled optical fibers), which guides information displayed on the screen of the display unit 110 to the vicinity of the key-top 120, is provided between the display unit 110 and the key-top 120.
According to this conventional switch device, when a plurality of functions are allotted to the key-top 120, the information 111 displayed on the screen of the display unit 110 is changed corresponding to a change of the functions so that the symbol of the key-top 120 can be changed accordingly, allowing a multiple display by the single key-top 120.
There are two types of general key-tops, a simple push-type (single push-type) as shown in FIG. 8A and a seesaw-type (double push-type) as shown in FIG. 8B. Regarding the conventional switch device, which is constructed in such a manner that a transparent key-top is arranged over a screen of a display unit, every key-top has been a simple push-type. A switch device equipped with a seesaw-type key-top has not been employed.
There are two reasons why a switch device equipped with a seesaw-type key-top has not been employed. One reason is that, as shown in FIGS. 9A and 9B, a seesaw-movement of a transparent key-top 140 requires that a center of the key-top 140 should be rotatively supported and, accordingly, that a space L1 is provided to receive a rotary shaft 141 and a bearing (not shown) between each adjacent key-top 140. However, it has been impossible to arrange a plurality of the key-tops 140 adjacently within a limited space over the screen of the display unit 110.
Another reason is that, as shown in FIG. 10, a pair of tactile switches 151 and 152 are needed to allow the transparent key-top 140 to be operable in two directions, such that the key-top 140 protrudes excessively from a face of the display unit 110, since a distance between the key-top 140 and the display unit 110 undesirably increases from L2 to L2+L3, where L2 is a height of the key-top 140 and L3 a height of the tactile switches 151 and 152.
Consequently, with vehicle-mounted equipment, in which the key-top 140 is seen from an oblique direction, a visual angle of information displayed on the screen of the display unit 110 cannot be ensured, resulting in a problem that the information displayed on the screen of the display unit 110 cannot be seen by an operator.
Thus, it has been impossible to realize the switch device equipped with a seesaw-type key-top that enables a multiple display and can be used for various purposes such as an equalizer, balancer and fader in a car-audio system, for example.